Method and apparatus for reducing defibrillation energy

ABSTRACT

An energy reduction unit is removably connectable to an external defibrillator to reduce the defibrillation energy delivered by the defibrillator to a patient. Use of the energy reduction unit is particularly suited to defibrillating pediatric patients (infants and children under 8) with an automatic or semi-automatic external defibrillator (AED). In one embodiment, the energy reduction unit includes an attenuator which partially dissipates energy produced by the AED. The attenuator is advantageously designed to present an impedance to the AED which, when connected to the patient, is approximately equal to the patient&#39;s impedance. The energy reduction unit may include a presence-detect function which enables the defibrillator to modify analysis of ECG signals to account for differences heart rhythms of pediatric and adult patients. In a second embodiment, the energy reduction unit includes an energy control modifier circuit which affects the charging operations performed internal to the AED. Other than being attached to the defibrillation equipment, the energy reduction unit does not otherwise change how an operator uses the equipment.

CONTINUING DATA

This application is a continuation-in-part of application Ser. No.08/775,827 filed Dec. 31, 1996 for "Method and Apparatus for ReducingDefibrillation Energy." Now abandoned.

TECHNICAL FIELD

This invention relates generally to a defibrillation method andapparatus, and more particularly to a method and apparatus for reducingthe electrical energy delivered by an external defibrillator."Defibrillators" include manual defibrillators, semi-automaticdefibrillators and automatic defibrillators. This invention also relatesto a method and apparatus for dynamically changing the operation of adefibrillator when treating a pediatric patient.

BACKGROUND OF THE INVENTION

Sudden cardiac death is the leading cause of death in the United States.Most sudden cardiac death is caused by ventricular fibrillation ("VF"),in which the heart's muscle fibers contract without coordination,thereby interrupting normal blood flow to the body. The only knowneffective treatment for VF is electrical defibrillation, in which anelectrical pulse is applied to the patient's heart. The electrical pulsemust be delivered within a short time after onset of VF in order for thepatient to have any reasonable chance of survival. Electricalfibrillation may also be used to treat shockable ventricular tachycardia("VT"). Accordingly, defibrillation is the appropriate therapy for anyshockable rhythm, i.e., VF or shockable VT.

One way of providing electrical defibrillation uses implantabledefibrillators, which are surgically implanted in those patients havinga high likelihood of experiencing VF. Implanted defibrillators typicallymonitor the patient's heart activity and automatically supply therequisite electrical defibrillation pulses to terminate VF. Implantabledefibrillators are expensive, and are used in only a small fraction ofthe total population at risk for sudden cardiac death.

External defibrillators send electrical pulses to the patient's heartthrough electrodes applied to the patient's torso. Externaldefibrillators are typically located and used in hospital emergencyrooms, operating rooms, and emergency medical vehicles. Of the widevariety of external defibrillators currently available, automatic andsemi-automatic external defibrillators (referred to collectively as"AEDs") are becoming increasingly popular because they can be used byrelatively inexperienced personnel. Such AEDs are also especiallylightweight, compact, and portable. AEDs are described in U.S. Pat. No.5,607,454 to Cameron et al. entitled "Electrotherapy Method andApparatus" and PCT Publication No. WO 94/27674 entitled "Defibrillatorwith Self-Test Features", the specifications of which are incorporatedherein.

AEDs provide a number of advantages, including the availability ofexternal defibrillation at locations where external defibrillation isnot regularly expected, and is likely to be performed quiteinfrequently, such as in residences, public buildings, businesses,personal vehicles, public transportation vehicles, etc. Althoughoperators of AEDs can expect to use an AED only very occasionally, theymust nevertheless perform quickly and accurately when called upon. Forthis reason, AEDs automate many of the steps associated with operatingexternal defibrillation equipment, and the operation of AEDs is intendedto be simple and intuitive: AEDs are designed to minimize the number ofoperator decisions required.

Because AEDs have primarily been designed to treat adult VF andshockable VT, AEDs are typically not recommended for treating pediatricpatients. One reason is that pediatric VF is not well documented andunderstood. For example, the optimal energy required for defibrillatinginfants and children has not yet been established--although currentlyavailable information suggests a starting dose of 2 J/kg. Additionally,the criteria used to analyze adult VF would not necessarily beappropriate for pediatric VF because of physiological differencesbetween adults and pediatric patients. Such differences include, forexample, heart rate. Finally, the protocol recommended for treating apediatric victim of sudden cardiac arrest is different than the protocolrecommended for treating an adult largely because pediatric VF istypically associated with respiratory failure. (See, Chameides et al.(Eds.) "Pediatric Advanced Life Support" (1997-1999) American HeartAssn).

FIG. 1 is a functional block diagram depicting an AED 20 and anelectrode unit 21. The electrode unit 21 includes defibrillationelectrodes 22 which are connected to a connector 23 by electrode wires25. In operation, an operator attaches the defibrillation electrodes 22to a patient 24, and plugs the connector 23 of the electrode unit 21into a connector 26 of the AED 20. The operator then turns on the AED20, and ECG signals are gathered by the electrodes 22 and routed to anECG amplifier 28 within the AED. An A/D converter 30 receives the analogoutput of the ECG amplifier 28, and provides corresponding digitalsamples to a microcomputer 32 for analysis. If the patient 24 iscurrently experiencing VF, the microcomputer 32 asserts a control signalto cause a high voltage charger 34 to transfer electrical energy from alow voltage source, such as a battery 36, to a high voltage energystorage device, such as a capacitor 38. In the case of semi-automaticAEDs, the operator is then prompted by the AED 20 to issue a shockcommand by depressing a shock control switch 39. In the case of fullyautomatic AEDs, the shock command is initiated by the microcomputer 32,and no shock control switch 39 is provided. In response to the shockcommand, the microcomputer operates a discharge switch 40 to deliver anelectric shock to the patient 24 through the electrodes 22.

As mentioned above, the use of AEDs for pediatric patients generally hasnot been considered, primarily because of concerns with potentialoperator confusion and machine complexity. When defibrillating pediatricpatients, the operator must know the appropriate energy dose to deliver,which is based on the pediatric patient's weight or age. In practicalterms, this means that an AED must have the necessary circuitry toaccurately produce at least two energy levels (adult and child). Becausethe AED cannot automatically detect the presence of a pediatric patient,the AED must provide the operator with a means, such as an energyselector switch, to choose the proper energy level. It is also necessarythat the AED properly analyze VF in pediatric patient. This may requirethe AED to be informed, via an operator action, that a pediatric patientis present in order to appropriately modify the ECG analysis to accountfor the differences between heart rhythms of pediatric and adultpatients. The need for an operator to select an appropriate energylevel, and to indicate to the AED whether a pediatric or adult patientis present, complicates both the AED design and the operator decisionmaking process each time the AED is used. Added complexity is ofparticular concern for first responder AEDs which are designed forinfrequent use, and are typically used by persons whose primaryoccupation is not lifesaving (such as police officers or flightattendants). Concerns regarding the possible consequences of suchcomplications have outweighed any expected benefits associated with thesmall utilization rate of AEDs for pediatric patients. Nevertheless, theinability to effectively treat an infant or child near death isdifficult to accept.

What is needed is a simple and effective way of reducing the amount ofenergy delivered to a pediatric patient by an AED. Additionally, what isneeded is a device that lowers the defibrillator energy delivered to apediatric patient as well as enables the defibrillator to modify itsbehavior to more effectively treat a pediatric patient. Additionally,what is needed is a device that enables the ECG analysis capabilities todynamically change when the pediatric energy reduction unit is in place.Finally, what is needed is a simple and effective way of reducing theamount of energy delivered to a pediatric patient by a traditional AED,but which allows a seamless hand-off to a manual defibrillator (or anAED with manual capabilities).

SUMMARY OF THE INVENTION

A method and apparatus is provided for reducing energy delivered by anexternal defibrillator to a child or infant patient. An energy reductionunit is removably connectable to the defibrillator. In one embodiment,the energy reduction unit includes an attenuator which partiallydissipates energy produced by the defibrillator. The attenuator may bedesigned to present an impedance to the AED which, when connected to thepatient, is a function of the patient's impedance. The energy reductionunit may also include a presence-detect function which enables thedefibrillator to modify ECG signal analysis to account for differencesbetween heart rhythms of pediatric and adult patients. Additionally, theenergy reduction unit may also change the care procedures thedefibrillator prompts the rescuer to follow. In a second embodiment, theenergy reduction unit includes an energy control modifier circuit whichaffects the charging operations performed internal to the AED. Once anoperator has determined that a pediatric patient falls below a selectedmeasurement threshold level, the operator connects the energy reductionunit to the defibrillator. All other steps performed by the operator areidentical to those steps performed when defibrillating an adult.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram depicting a prior art automatic orsemi-automatic external defibrillator (AED).

FIG. 2 is a functional block diagram depicting an energy reduction unit,according to the present invention, used in combination with the AED ofFIG. 1.

FIG. 3A is a plan view depicting a first electrical connector structureof the energy reduction unit of FIG. 2.

FIG. 3B is a plan view depicting an electrode system incorporating anenergy reduction unit.

FIG. 4 is a plan view depicting a second electrical connector structureof the energy reduction unit of FIG. 2.

FIG. 5 is a functional block diagram depicting a first embodiment of theenergy reduction unit of FIG. 2, and includes an attenuator.

FIG. 6A is a schematic diagram depicting a preferred embodiment of theattenuator of FIG. 5.

FIG. 6B is a schematic diagram depicting an alternate embodiment of theattenuator of FIG. 5.

FIG. 6C is a schematic diagram depicting another alternate embodiment ofthe attenuator of FIG. 5.

FIG. 7 is a functional block diagram depicting a second embodiment ofthe energy reduction unit of FIG. 2, and includes a presence-detectcapability.

FIG. 8 is a functional block diagram depicting a third embodiment of theenergy reduction unit of FIG. 2, and includes an energy controlmodifier.

FIG. 9 is a perspective view of an alternate embodiment of the energyreduction unit shown in FIGS. 3 and 4.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment, an energy reduction unit is described which isremovably connectable to currently available AEDs and which provides themeans for effectively treating pediatric patients with an AED, butwithout otherwise complicating AED design or operator interaction. Theenergy reduction unit reduces the amount of electrical energy deliveredto a pediatric patient by an AED. As used herein, "pediatric" includesall children under the age of 8. Typically, "pediatric" is furtherdivided into two sub-groups: "infant" (0-1 yr) and "child" (1-7 yr). Inthe following description, certain specific details are set forth inorder to provide a thorough understanding of the preferred embodiment ofthe present invention. It will be clear, however, to one skilled in theart that the present invention may be practiced without these details.In other instances, well-known circuits have not been shown in detail inorder not to unnecessarily obscure the description of the variousembodiments of the invention. Also not presented in any detail are thosewell-known control signals and signal timing protocols associated withthe internal operation of AEDs.

Referring to FIG. 2, an energy reduction unit 50 is shown in combinationwith the AED 20 described above in connection with FIG. 1. The energyreduction unit 50 is removably connectable to the connector 26 of theAED 20, by virtue of having a connector 51 of the same configuration asthe connector 23 of the electrode unit 21. The energy reduction unit 50also includes a connector 52, of the same configuration as the connector26 of the AED 20, to provide for connection to the connector 23 of theelectrode unit 21. Although FIG. 2 depicts the energy reduction unit 50used in combination with the electrode unit 21 ordinarily used onadults, those skilled in the art will appreciate that pediatric-specificelectrodes (both "child" and "infant") may be used which are, forexample, sized differently than adult electrodes. Also, while FIG. 2depicts the energy reduction unit 50 as separate from and connectable tothe electrode unit 21, those skilled in the art will appreciate thatpediatric-specific electrode units may be designed which integrate oneor more of the energy reduction unit features (described below) withinthe electrode unit itself.

Other than the simple placement of the energy reduction unit 50 betweenthe AED 20 and the electrode unit 21, performing defibrillation for apediatric patient 54 may be the same as the procedure for an adultpatient 24, as outlined above in connection with FIG. 1. No additionaloperator procedure complexity or AED design complexity need beintroduced.

When treating a pediatric patient with the energy reduction unit shownin FIG. 2, the rescuer connects the connector 23 of the electrode unit21 to the energy reduction unit 50 and then connects the resultingcombination to the AED 20. All other aspects of operating the AED remainthe same. As a result, the only additional step taken by the rescuer isattaching the energy reduction unit 50. This additional step results inlower energy being delivered to the patient without unnecessarilycomplicating the procedure or increasing the cost of the defibrillator.

To appreciate some of the advantages achieved by use of the energyreduction unit 50 when defibrillating a pediatric patient, considerinstead an AED designed to include an energy selector switch. Inaddition to increasing the complexity of the AED design, an operator ofthe AED would have to determine the appropriate setting of the energyselector switch each time the AED is used. In the event of operatorerror, an adult experiencing VF would then receive an inappropriatelylow energy defibrillation pulse, and the defibrillation procedure couldbe unsuccessful. Conversely, in the event of an operator error, apediatric patient may receive an inappropriately high energydefibrillation pulse, with possible adverse consequences. Defibrillatinga pediatric patient is unusual, and ideally it should be unnecessary torequire an operator of an AED to consider the unusual case in every useof the instrument. In accordance with the present invention, theoperator of an AED need only consider the steps associated withdefibrillating a pediatric patient in the event that such an action isactually required. In the unusual case of defibrillating a pediatricpatient, the operator performs a correspondingly unusual action--namely,connecting a pediatric-specific electrode unit and/or energy reductionunit to the AED.

FIGS. 3A, 3B and 4 depict alternate connector/housing structures for theenergy reduction unit 50. Each shows a similarly constructed circuithousing 56 with the connector 52 suitable for receiving the connector 23of the electrode unit 21 (see FIG. 1). The circuit housing 56 has a flatconfiguration to permit easy storage, and to permit a large, graphicallabel 57 describing the proper use of the energy reduction unit 50. FIG.3A shows the connector 51 of the energy reduction unit 50 mounteddirectly on the circuit housing 56. FIG. 3B shows an energy reductionelectrode assembly which includes electrodes formed with an energyreduction unit 50. FIG. 4 shows the connector 51 of the energy reductionunit 50 connected to the circuitry within the circuit housing 56 via acable 58 (which may be retractable, as desired). The length of the cable58 is selected to correspond with the average height of a child weighing25 kilograms (a conventional threshold value) or infant. Additionally,one cable length may be provided which contains markings to indicate theheight for an infant and a child. In this way, an operator can quicklyand easily determine whether the energy reduction unit 50 should beemployed, or whether the pediatric patient should be defibrillated as anadult.

When treating a pediatric patient with the energy reduction unit shownin FIG. 3A, the rescuer connects the connector 23 of the electrode unit21 (shown in FIG. 2) to the energy reduction unit 50 at connector 52 andthen connects the resulting combination to the AED 20 (also shown inFIG. 2). All other aspects of operating the AED remain the same. As aresult, the only additional step taken by the rescuer is attaching theenergy reduction unit 50.

Alternatively, when treating a pediatric patient with the energyreduction unit shown in FIG. 3B, the rescuer connects the connector 51of the electrode assembly to the AED 20 (shown in FIG. 2). All otheraspects of operating the AED remain the same. As a result, no additionalsteps are required aside from selecting the appropriate electrodes(e.g., electrodes with an energy reduction unit or without).

When treating a pediatric patient with the energy reduction unit of FIG.4, the rescuer uses the cable 58 as a gauge to measure the height of thepatient. Two lengths, one for an infant and one for a child may beemployed. Alternatively, one length may be used which provides anindication of the length of an infant and a child. If, for example, theheight of the patient exceeds the cord length for an infant, then therescuer knows that the child energy reduction unit 50 should beemployed. If, however, the height of the patient exceeds the cord lengthfor a child, then the rescuer knows that the standard adult electrodesshould be used and the energy reduction unit is not required. All otheraspects of operating the AED remain the same.

FIG. 5 depicts a first embodiment of the energy reduction unit 50 andincludes an attenuator 60. The attenuator 60 partially dissipates theenergy produced by the AED 20 to provide a child-appropriate orinfant-appropriate energy level at the electrodes 22. For example, atypical AED supplies a fixed output energy of not less thanapproximately 130 J, which is a suitable energy for adults. When used ona child, the attenuator 60 dissipates approximately 80 J of energy anddelivers the remaining 50 J to the child patient--an appropriate dosefor children up to 25 kilograms in weight. When used on an infant, theattenuator 60 dissipates 115 J of energy and delivers the remaining 25 Jto the infant. For children over 25 kilograms, the energy reduction unit50 is not employed and the adult energy level is delivered.

FIG. 6A is a schematic diagram which depicts a first preferredembodiment of the attenuator 60. Included are first and second sparkgaps VSP₁ and VSP₂ which are placed in series with a resistor R₁ betweenfirst and second signal lines 62, 64. The signal line 62 connects theconnector 51 with the connector 52 and includes a resistor R₂. Thesignal line 64 also connects the connector 51 with the connector 52 andincludes a resistor R₃. For purposes of minimizingcommon-to-differential mode conversion effects, R₂ and R₃ are shown asseparate resistors, and are of equal value, but could also be combinedinto a single resistor in either of the signal lines 62, 64. Similarly,two spark gaps VSP₁ and VSP₂ are used to minimize the effects of commonmode currents, but a single spark gap could suffice.

Normally, when a patient's ECG is being monitored and analyzed, thepatient's equivalent circuit in series with the electrodes is a highimpedance source of approximately 10 kΩ and 1 mV. When this signal istransmitted through the signal lines 62, 64, the spark gaps VSP₁ andVSP₂ are non-conducting and appear as an open circuit. The selectedresistance values of resistors R₂ and R₃ are such as to have noappreciable effect on the high impedance ECG signal delivered from thepatient to the ECG amplifier 28 within the AED 20 (see FIG. 2).

During defibrillation energy delivery, a high voltage is applied (e.g.,approximately 1700V-2100V, more preferably 1800V). The equivalentpatient circuit then appears to be of relatively low impedance, varyingfrom approximately 50 to 125Ω with a mean of approximately 75Ω. Duringdefibrillation, the high voltage pulse shorts spark gaps VSP₁ and VSP₂,thus introducing the resistor R₁ as a shunt resistance. Those skilled inthe art will appreciate that the spark gaps VSP₁ and VSP₂ function asvoltage-sensitive switches, such that a high applied voltage promotesconduction therethrough. This function can be accomplished by numerousother well-known means. For example, one or more diodes may be employedwhich become(s) forward biased when a high voltage is applied.

It is desirable that the equivalent circuit of the patient 54 (see FIG.2) plus attenuator 60 present an impedance indicative of the patient'sactual impedance. Also, it is desirable that, of the 130 J produced bythe AED 20, approximately 50 J is delivered to the patient 54. Thevalues of the resistors R₁, R₂, and R₃ are calculable accordingly. For atypical patient impedance of approximately 75Ω, the value of R₁ isapproximately 220Ω and the values of R₂ and R₃ are each approximately20Ω. For these resistance values, and given the typical range of patientimpedances, the impedance presented to the AED 20 varies fromapproximately 60Ω to 100Ω. The impedance presented to the defibrillatorthrough the energy reduction unit 50 is thus a function of the actualpatient impedance. The energy delivered to the patient is relativelyconstant, varying only slightly in a range from approximately 50 to 60Joules.

FIG. 6B shows a second preferred embodiment of the schematic of theenergy reduction unit wherein resistors R₁, R₂, and R₃ are controlled byswitches, SW₁, SW₂, and SW₃, respectively. When switches SW₁ is open andswitches SW₂ and SW₃ are closed, the energy is not attenuated. Whenswitch SW₁ is closed and switches SW₂ and SW₃ are open, the energy isattenuated. When the energy reduction unit is initially attached, switchSW₁ is closed and switches SW₂ and SW₃ are open, thus allowing theenergy to be attenuated. The switch positions are only reversed if, forexample, the rescuer later activates a disarm button (providedexternally on the energy reduction unit). The switch positions may alsochange as a result of connecting to an AED or manual defibrillator. Forexample, when a later arriving advanced cardiac life support ("ACLS")responder arrives (with a manual defibrillator or semi-automaticdefibrillator with manual capabilities), the ACLS responder need onlyoverride the attenuation feature of the energy reduction unit 50. As aresult, the ACLS responder can inactivate the energy reduction unit 50without removing the unit or the electrode pads attached to the patient.Depending upon how the energy reduction unit 50 has been configured, theinactivation can occur automatically when the energy reduction unit 50is connected to a defibrillator capable of manual settings, or manually,by the activation of a disarm button provided on the energy reductionunit 50. All other functions of the circuit are as described above withrespect to FIG. 6A.

FIG. 6C shows a third preferred embodiment of the energy reduction unit50. Instead of a single resistor R₁ in series between the first andsecond spark gaps, VSP₁ and VSP₂, two resistors R₁ and R₄ are providedin parallel, where R₁ delivers infant energy and R₄ delivers childenergy. Each resistor is controlled by a switch, shown as SW₁, SW₂, SW₃and SW₄, respectively. Again, operation of the switches may becontrolled by the operator or may occur automatically when the connectoris attached to an AED or a manual defibrillator. When switches SW₁ andSW₄ are open and switches SW₂ and SW₃ are closed, energy is notattenuated. When switch SW₁ is closed, and switches SW₂, SW₃ and SW₄ areopen, then resistor R₁ is in series between the spark gaps VSP₁, andVSP₂ resulting in the energy delivered by the defibrillator beingattenuated and delivery of an energy appropriate for an infant. Whenswitch SW₄ is closed, and switches SW₁, SW₂ and SW₃ are open, thenresistor R₄ is in series between the spark gaps VSP₁ and VSP₂, resultingin an energy attenuation and delivery of an energy appropriate for achild. All other functions of the circuit are as described above withrespect to FIG. 6A.

FIG. 7 depicts a second embodiment of the energy reduction unit 50, inwhich a presence-detect function has been added. This requires arelatively straightforward change to the design of the AED 20 to providea presence-detect connector 62 and to provide presence-detectfunctionality to the microcomputer 32. Of course, the presence-detectconnector 62 of the AED 20 can simply be additional pins or theequivalent integrated into the connector 26, as desired. Thepresence-detect connector 62 of the AED 20 receives a connector 64 ofthe energy reduction unit 50. Similarly, the connector 64 can beintegrated as additional pins or equivalent into the connector 51 of theenergy reduction unit 50.

In the example implementation depicted in FIG. 7, a simple signal loop66 is provided which routes a presence-detect signal provided by themicrocomputer 32 back to the microcomputer. In this way, themicrocomputer 32 is informed of the presence of the energy reductionunit 50. Accordingly, the microcomputer 32 can modify analysis of thepatient's ECG, to appropriately account for differences between theheart rhythms of pediatric and adult patients. The microcomputer 32 mayalso change the protocol followed and voice prompts presented to therescuer in response to the appearance of the energy reduction unit 50.

In another embodiment of the signal loop 66 can route a differentpresence-detect signal for infant and child patients, thus allowing thedefibrillator to further refine the ECG analysis, voice prompts orprotocol.

Where the presence detect circuit is incorporated into the electrodes, aseparate circuit can be provided for each electrode type (e.g., adult,child or infant). By integrally forming the presence detect circuit withthe electrodes, each electrode type can actively be identified by thedefibrillator.

Those skilled in the art will appreciate that a presence-detect functioncan be provided by transmitting any of a wide variety of signals fromthe energy reduction unit 50 to the AED 20. For example, an optical orother electromagnetic signal can be used. Additionally, a mechanicalsignal can provide the presence-detect function, such as a portion ofthe connector 64 extending within the AED 20 to mechanically trip aswitch. Finally an ID chip may be provided that communicates with thedefibrillator to identify the electrode type or the presence and type ofenergy reduction unit.

In addition to signaling to the microcomputer 32 that ECG analysis mustbe modified, the presence-detect function may itself signal to themicrocomputer 32 that a reduced energy delivery is required. In thisway, the energy reduction unit 50 need not include the attenuator 60(see FIG. 5) or other energy reducing circuitry--the reduction of energydelivery instead being accomplished by circuitry within the AED 20itself. No increased operator complexity results from such animplementation, but a more complicated (and correspondingly moreexpensive) AED unit is required. An advantage of this embodiment is thatthe defibrillator can, in addition to lowering energy, also change thepatient ECG analysis as well as the voice prompts and treatment protocolrecommended by the defibrillator.

FIG. 8 is a functional block diagram which depicts a third embodiment ofthe energy reduction unit 50. In this case, no dissipation or otherattenuation of energy is accomplished internal to the energy reductionunit 50. Instead, an energy control modifier circuit 68 causes the highvoltage charger 34 to cease charging the capacitor 40 at a lower voltagethan when the energy control modifier circuit 68 is not present. Theenergy control modifier circuit 68 could include a comparator circuit ora resistor network and appropriate sensors, as will be clear to thoseskilled in the art. This embodiment is particularly suited to AEDs inwhich the operations of the high voltage charger 34 are not directlysensed and controlled by the microcomputer 32. Alternatively, the energycontrol modifier circuit 68 could assert a control signal to themicrocomputer 32 or other circuitry within the AED 20 to effect a changeof energy storage operations within the AED.

Additionally, the energy reduction unit 50 can contain program memoryusable by the AED to appropriately modify the patient treatmentprotocol. For example, circuitry block 68 may contain read-only memorythat is readable by microcomputer 32 when the energy reduction unit 50is attached to the defibrillator. In use, the microcomputer 32 wouldfollow instructions provided by memory in circuitry block 68 in order tofollow a treatment protocol other than the default program of AED 20.This has the advantage of allowing the AED's protocol of operatorinteractions, voice prompts, delivered treatments, ECG analysis, andother factors to be modified when an energy reduction unit is connectedto the AED. Thus, as treatment evolves (for example, a new recommendedprotocol for treating pediatric cardiac arrest victims), the AED ownercan receive the benefits of upgraded treatments automatically byobtaining relatively inexpensive accessory modules.

FIG. 9 depicts a removable electrical connector 50, similar to theconnector 50 shown in FIG. 3, except that it additionally provides aremovable projection 102 on the connector 50. The removable projection102 does not impede the ability of the connector 50 from being used withan AED. However, the removable projection 102 does prevent the connectorand associated electrodes from attaching to a manual defibrillator, oran AED with manual capabilities without first removing the projection102.

The operation of the energy reduction unit of FIG. 9 is substantiallythe same as the operation described with respect FIGS. 3 and 4. Theadvantage of the energy reduction unit of FIG. 9 is the removableprojection 102. When a pediatric victim of sudden cardiac arrest istreated by a first responder using an AED which has been adapted toinclude the energy reduction unit, the AED delivers less energy to thepediatric patient as a result of the energy reduction unit. A laterarriving ACLS responder (such as a second tier responder) will likelyhave either a manual defibrillator or an AED with manual capabilities.Since manual defibrillators can be set to deliver, for example, lessenergy, it would not be desirable to allow a pair of electrode pads withan energy reduction unit to be attached to a manual defibrillatorbecause the manual defibrillator may be set to deliver the correctpediatric energy, but that energy would then be reduced by the energyreduction unit, thereby resulting in an ineffective shock. By providinga removable projection, the ACLS responder is alerted to the fact thatthe energy reduction unit was in place and could either remove theprojection and deliver adult energy (knowing it would be reduced) orremove the energy reduction unit and deliver a reduced amount of energy.

The function and interconnection of a number of circuits are describedabove. These circuits are known in the art, and one skilled in the artwould be able to use such circuits in the described combination topractice the present invention. The internal details of these particularcircuits are not part of, nor critical to, the invention, and a detaileddescription of the internal circuit operation need not be provided.

While certain embodiments of the invention have been described forpurposes of illustration, various modifications may be made withoutdeviating from the spirit and scope of the invention. For example, theuse of the energy reduction unit 50 has been described in connectionwith automatic and semi-automatic external defibrillators. However, thepresent invention can be advantageously used with a wide variety ofexternal defibrillation equipment. Also, a particular attenuatorconfiguration has been described in detail in connection with FIGS. 5and 6. However, those skilled in the art will understand that a widevariety of circuits may be employed which partially dissipate the energyproduced by a defibrillator, while presenting an impedance to thedefibrillator which is a function of the patient impedance. Further,connector structures have been depicted schematically and describedgenerally. Those skilled in the art will understand that any of numerousconnector types may be used. Indeed, numerous variations are well withinthe scope of this invention. Accordingly, the invention is not limitedexcept as by the appended claims.

What is claimed is:
 1. An apparatus removably connectable between adefibrillator and a pair of electrodes, the defibrillator capable ofdefibrillation operations, the operations including deliveringdefibrillator energy to an exterior surface of a patient, the apparatuscomprising:an energy reduction unit having a read-only memory thatprovides a control signal, the control signal including information fromthe read-only memory, to the defibrillator and which is operable toautomatically reduce defibrillation energy producing operations of thedefibrillator.
 2. The apparatus of claim 1 wherein the energy reductionunit is adapted to reduce 80 Joules of energy.
 3. The apparatus of claim1 wherein the energy reduction unit is adapted to reduce 115 Joules ofdefibrillation energy.